Fabrication and characterization of Si_1−xGe_x nanocrystals in as-grown and annealed structures: a comparative study

Abstract

Multilayer structures comprising of SiO2/SiGe/SiO2 and containing SiGe nanoparticles were obtained by depositing SiO2 layers using reactive direct current magnetron sputtering (dcMS), whereas, Si and Ge were co-sputtered using dcMS and high-power impulse magnetron sputtering (HiPIMS). The as-grown structures subsequently underwent rapid thermal annealing (550–900 °C for 1 min) in N2 ambient atmosphere. The structures were investigated using X-ray diffraction, high-resolution transmission electron microscopy together with spectral photocurrent measurements, to explore structural changes and corresponding properties. It is observed that the employment of HiPIMS facilitates the formation of SiGe nanoparticles (2.1 ± 0.8 nm) in the as-grown structure, and that presence of such nanoparticles acts as a seed for heterogeneous nucleation, which upon annealing results in the periodically arranged columnar self-assembly of SiGe core–shell nanocrystals. An increase in photocurrent intensity by more than an order of magnitude was achieved by annealing. Furthermore, a detailed discussion is provided on strain development within the structures, the consequential interface characteristics and its effect on the photocurrent spectra.

Optimizing SiGe–SiO2 Visible–Short‐Wave Infrared Photoresponse by Modulating Interplay Between Strain and Defects Through Annealing

“…For thick S FA* samples (≈200 nm SiGe film) (Figure 4a) annealed in furnace, the stress field developed is partially relaxed by the formation of defects in NCs mainly by coalescence of small NCs during annealing. [3] In Figure 4b, SiGe NCs size are evaluated from the lattice fringe contrast and it is similar to that obtained from XRD measurements. In contrast to thin S FA structure, the film is polycrystalline, uniform, and shows no texture.…”

“…The formation of such quasiperiodic NCs has been attributed to the crystallization process during annealing which develops a stress field in the SiGe plane along with the strain exerted by the SiO 2 matrix resulting in the formation of corrugated edges by strain relaxation. [3,47] The average size of the NCs is ≈10 nm with ≈2-5 nm distance between them (Figure 3b) comprising amorphous SiGeO x with Si excess by oxygen diffusion from the surrounding oxide matrix, thus forming the intercolumnar film. The Si excess in SiGeO x is explained in literature by SiO 2 formation that is more exothermic than that of GeO 2 and annealing at elevated temperatures will result in Ge segregation, leading to Ge-rich SiGe NCs.…”

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Over the past decades, substantial studies have been made on self-assembled Si 1Àx Ge x nanocrystals (NCs) in oxide matrices such as SiO 2 , [1][2][3] and high-dielectric-constant oxides such as TiO 2 , [4,5] Al 2 O 3 , [6] and HfO 2 . [7] Of these, SiO 2 is the most studied, as it remains amorphous and provides lateral confinement to the NCs up to high annealing temperatures.

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Structural and optical characteristics determined by the sputtering deposition conditions of oxide thin films

“…SiO 2 and ZnO films are obtained by various deposition techniques, such as matrix-assisted pulsed laser evaporation (MAPLE) [24,25], spin coating of sol-gel precursor solutions [26], radio-frequency magnetron sputtering (rfMS) [27][28][29][30], vacuum thermal evaporation (VTE) [31][32][33], chemical methods [34], reactive ion beam sputter deposition [35], among others. For example, SiO 2 and ZnO films obtained by rfMS can be either used as dielectric materials in metasurface structures or as dielectric interfaces in the structure of a metamaterial.…”

Structural and optical characteristics designed by sputtering deposition conditions of the oxide thin films

“…The SiO2 and ZnO films are obtained by various deposition techniques, such as: matrix-assisted pulsed laser evaporation (MAPLE) [24,25], spin coating of sol-gel precursor solutions [26], radio frequency magnetron sputtering (rfMS) [27][28][29][30], vacuum thermal evaporation (VTE) [31][32][33], chemical methods [34], reactive ion beam sputter deposition [35] etc. For example, SiO2 and ZnO films obtained by rfMS technique can be used as dielectric materials in metasurface structures, or as dielectric interfaces into the structure of a metamaterial.…”